docs: def propagate(self, year, month=1, day=1, hour=0, minute=0, second=0.0):
          """Return a position and velocity vector for a given date and time."""
  
          j = jday(year, month, day, hour, minute, second)
          m = (j - self.jdsatepoch) * minutes_per_day
          r, v = sgp4(self, m)
          return r, v